1. Field of the Invention
An aspect of the present invention relates to a power supply circuit.
2. Description of the Related Art
A ferroelectric memory as one of nonvolatile semiconductor storage devices has a plurality of internal power supply voltage generation circuits provided in a chip to select a memory cell and to control a storage operation. These internal power supply voltages are controlled to start generating an internal power supply voltage when an external power supply is turned on and an external power supply voltage exceeds a predetermined voltage. For that purpose, a power supply turn-on detection circuit for detecting turn-on of the external power supply is provided in the chip.
A reading operation of reading out data stored in such a ferroelectric memory is a destructive reading operation of destroying data stored in a memory cell. This causes a problem that upon interruption of an external power supply in the middle of a reading operation, data stored in a memory cell is destroyed by occurrence of an access to the memory cell.
Thus, it is desired for preventing such destruction of data that when an external power supply voltage is equal to or lower than a predetermined value, at least an internal power supply voltage to be supplied to a memory cell array becomes 0 V.
Thus, a power supply voltage detection circuit for detecting a change in the external power supply voltage has hitherto been provided in a chip to enable the detection of interruption of the external power supply in addition to the turn-on of the external power supply. Consequently, the activation and the discharging of the internal power supply voltage generation circuit are controlled (see, e.g., JP-2003-196974-A).
However, sometimes, an external power supply voltage drops due to noise or the like only for a short time. Thus, a conventional power supply circuit has a problem in that when the internal power supply voltage supplied to a memory cell array is discharged to 0 V in such a case, it takes long time to restore the voltage and increases power consumption.